This invention relates to the fixation of dissolved metal species, e.g., radioactive cationic species, with a complexing agent immobilized on a support such as a silicate glass or silica gel or charcoal matrix.
A number of radioactive isotopes are present in the cooling, operational and waste water from the daily operation of nuclear power plants and fuel rod holding tanks. While these radioactive isotopes are present in the water in very low concentrations, they are nonetheless highly radioactive and toxic to human life. Safe disposal or re-use of the contaminated water can only be conducted if a sufficient quantity of radioactive isotopes is removed to reach permissible levels.
The production of Co.sup.60 and Co.sup.58 through neutron activation of stainless steel is prevalent in most power reactors. These isotopes of cobalt migrate through the various waste streams in the reactor and eventually contaminate the waste waters. Accordingly, the removal of radioactive cobalt is important in the waste water treatments prior to release into the environment.
Waste water often represents a mixture of primary coolant containing such radioactive ions as Co.sup.58 and Co.sup.60 as well as fission fragments such as I.sup.131, Cs.sup.137 and Cs.sup.134 with other streams which may have high concentrations of ions. Those reactors cooled by coastal waters will have a significant content of sea water. Typical sea water contains approximately 10.5 g/l Na, 1.35 g/l Mg, 0.40 g/l Ca, 0.38 g/l K, 19.0 g/l Cl, 2.65 g/SO.sub.4 and 0.065 g/l Br.
Strong acid cation resins effectively remove ionic cobalt from aqueous media having low ionic content. However, if a significant amount of water with high concentrations of ions, e.g., sea water or "hard" ground water, enters the stream, it will exhaust the resin after a relatively small number of column volumes. Thus, in order to reduce the amount of waste (spent ion exchange media), it would be desirable to develop a selective ion exchange material that will pick up Co in the presence of Na, K, Ca, Mg, etc.
Furthermore, sea water contains large concentrations of anions such as chloride and sulfate which form complexes with Co. Most of these complexes are univalent or neutral, and therefore they are less amenable to sorption by ordinary ion exchangers than the divalent Co ion.
The removal of radioactive cations such as cobalt using a porous glass cation exchanger is disclosed in co-pending application of one of the present inventors Ser. No 370,437, filed Apr. 21, 1982, now U.S. Pat. No. 4,469,628, which is a continuing application of Ser. No. 39,595, filed May 16, 1979, now abandoned, which is a continuing application of Ser. No. 959,222, filed Nov. 9, 1978, now abandoned, each by Simmons, Simmons, Macedo and Litovitz and each entitled "Fixation By Ion Exchange of Toxic Materials In A Glass Matrix". The porous glass media disclosed in the co-pending application will effectively remove Co from streams with high concentrations of Na and K. Even though very useful in many cases where the concentrations of Na and K are high while the Ca and Mg concentrations are low, the porous glass media have limitations when either Ca or Mg or both are high in concentration.
Several patents describe the use of complexing agents in the decontamination of solid surfaces and liquid streams contaminated with radioactive isotopes in nuclear facilities. U.S Pat. No. 3,047,434 describes a solution for radioactive decontamination comprising a mixture of water, ethylenediaminetetraacetic acid, sodium sulfate, sodium hydroxide, manganese dioxide and carbon black. The patent also describes a decontamination method which comprises immersing a radioactively contaminated article in a solution comprised of water, ethylenediaminetetraacetic acid, sodium sulfate, sodium hydroxide, manganese dioxide and carbon black, and subjecting said solution to ultrasonic vibration forces sufficient to produce cavitation therein. The invention relates to the decontamination of solid articles contaminated with radioactive species exemplified by cesium 134. Other adsorbents mentioned as being of possible use as ingredients of decontamination solutions in addition to manganese oxide and carbon black are silicates such as a colloidal clay, talc, and fuller's earth, chalk; sulfides of arsenic and antimony; diatomaceous earth; and metallic oxides such as alumina, magnesia, iron oxide and titanium dioxide.
U.S. Pat. No. 3,080,262 describes a process effective for removal of radioactive contaminants from a surface which comprises contacting said surface with an aqueous solution which consists essentially of an alkali and an alkanolamine, and removing radioactive contaminants from said surface. In particular, the decontamination solution consists essentially of from about 5% to about 55% by weight of an alkali metal hydroxide (such as potassium hydroxide), from about 1% to about 45% by weight of an agent taken from the group consisting of soluble salts of the aliphatic hydroxy acids and soluble salts of the low molecular weight fatty acids (such as potassium acetate or potassium hydroxyacetate) and from about 2.5% to about 30% by weight of an alkanolamine (such as triethanolamine). Ethylenediamine derivatives such as tetrakis-N-(2-hydroxypropyl) ethylenediamine are added as minor ingredients to some of the solutions mentioned in the examples.
U.S. Pat. No. 4,222,892 describes a process for preparing oxine (8-hydroxyquinoline) adsorbed - activated charcoal which comprises contacting solid oxine with activated charcoal in the air or in water until the activated charcoal becomes impregnated with the oxine. This patent mentions a method of removing radionucleides from the cooling and leakage-water from nuclear reactors. The principle of this method comprises adding an oxine into the cooling-water of the nuclear reactor or leakage-water therefrom to form water-insoluble and stable complexes of the radionucleides contained therein and adsorbing them on activated charcoal. Many kinds of operations can be employed in the method, for example an operation using activated charcoal on which oxine is adsorbed, a batchwise operation in which activated charcoal is added after addition of oxine, or a continuous operation using an activated charcoal column. However, the operation using activated charcoal on which an oxine is impregnated is recommended. A mention is also made of a method or removing heavy metals such as mercury, copper, chromium, etc., from a water solution containing the heavy metals using an activated charcoal or silica gel on which oxine is adsorbed and carried.
Ralph K. Iler "The Chemistry of Silica" (Wiley-Interscience, New York, 1979, pp. 672-676) surveys the literature pertaining to adsorption of metal ions on silica, in most cases hydroxylated silica. In several cases it reports that metal ions complexed by organic ligands can be adsorbed on silica surfaces. These include the ethylenediamine complexes of thallium, silver, nickel, cobalt, copper and zinc. All the studies quoted in this review consist of experiments where a metal ion is reacted with a dissolved organic compound in aqueous solution, and the usually slow adsorption of the resulting complex species on a silica surface is monitored.
Thus, it is an object of this invention to make sorption media which will remove dissolved metal species such as Co atoms and/or ions from aqueous streams. Another object of this invention is to make sorption media which will remove dissolved metal species such as Co atoms and/or ions from aqueous streams in the presence of large excess amounts of Na, K, Ca, Mg and other ions and/or in the presence of large excess amounts of chloride, sulfate and other species which can form complexes with cobalt. In addition to the removal of radioactive metal species, it also is an object to remove dissolved metal species from non-radioactive streams such as cleaning and metallic plating solutions and hydrometallurgical solutions.